A device of this type is known from document FR 2 263 362. Such a device includes a U-shaped support that is open downwardly, the web of the U-shape being directed towards the bottom of the panel or being constituted by the bottom portion of said panel. The oscillating arm is secured to the support by means of a pivot pin which is both horizontal and transverse relative to the U-shape. The roller wheel is secured near the free end of the oscillating arm. Rotation of the pivot cam serves to cause the oscillating arm to pivot about its axis. Displacement of the adjustment screw, by rotation of the screw, enables the angle of rotation of the cam to be adjusted.
In the above-specified prior document, the cam is mounted on the oscillating arm and consists in a T-shaped bearing element having one arm that bears against the web of the U-shape and whose other arm bears against the free end of the threaded shank constituting the adjustment screw, which screw is generally also mounted on the oscillating arm. Thus, to adjust the height of the roller wheel, the user rotates the adjustment screw, thereby displacing the threaded shank of said screw relative to the oscillating arm, with the free end of the screw bearing against the second arm of the cam. This causes the cam to rotate because the first arm is bearing against the web of the U-shape, thereby causing the oscillating arm to rotate since it is secured to the axis of rotation of said cam.
In the embodiment proposed in prior document FR 2 263 362, as explained above, the adjustment screw is secured to the oscillating arm such that said screw follows any motion imparted to said oscillating arm throughout adjustment. According to the Applicant, this constitutes a drawback insofar as it is not very convenient for a user to perform an adjustment operation and, above all, insofar as the screw rapidly becomes difficult to access when the oscillating arm is in a low position.